The technical development of full-color copiers in recent years has made it possible even for ordinary users to readily perform copying in which the image quality of the copy is not that much different from that of the original. There is the fear that originals such as banknotes and negotiable instruments whose copying is prohibited by law may be counterfeited by making unlawful use of such full-color copiers.
In a known technique proposed in order to prevent such counterfeiting of originals, all or part of a specific original such as a banknote or negotiable instrument is stored in a copier beforehand as a distribution in color space or as a spatial pattern. When a copying operation is performed, discrimination processing (pattern matching) to determine whether an original is such a specific original is executed and the copying operation is inhibited if it is determined that the original is a specific original.
With the conventional technique described above, the usual practice is to subject the entirety of the specific original to pattern matching or to extract an image pattern from the specific original and subject this pattern to matching processing. However, if, when the original is read, the original to be copied is read in an orientation that differs from the assumed orientation, it is necessary to deal with the orientation (rotation) of the original. This means that it is necessary for image patterns that have been rotated through a number of different angles to be retained beforehand in the copier as templates, and it is required that pattern-matching processing be repeated a number of times equivalent to the number of templates when a copying operation is carried out.
Further, in order to arrange it so that banknotes or negotiable instruments of a greater number of types can be discriminated, a commensurate number of templates must be retained within the copier. As a consequence, a larger memory capacity is needed to hold these templates and a problem that arises is a very large increase in cost.
In addition, in order to prevent the copying of a specific original with the conventional technique described above, the templates that have been stored in the copier must be updated or added to whenever there is an increase in the types of specific originals whose copying is prohibited. This makes management difficult.